1. Field of the Invention
The present disclosure relates to a method and an apparatus for making a metallic casing, particularly, for making a metallic casing used in portable electronic devices.
2. Discussion of the Related Art
Metallic casings are considered attractive candidates for use in various portable electronic devices such as an MP3 player, personal digital assistance (PDA), and mobile phone because of their sturdiness and appealing appearance.
Referring to FIG. 6, a typical metallic casing 10a includes an approximately rectangular base 11a, a first sidewall 12a, a second sidewall 13a, a third sidewall 14a, and a fourth sidewall 15a. The first sidewall 12a, the second sidewall 13a, the third sidewall 14a, and the fourth sidewall 15a all extend around a periphery of the base 11a. The first sidewall 12a, the second sidewall 13a, the third sidewall 14a, and the fourth sidewall 15a respectively connect to each other. The first sidewall 12a, the second sidewall 13a, the third sidewall 14a, the fourth sidewall 15a, and the base 11a cooperatively define a cavity (not labeled) with an opening. The cavity is configured for receiving electronic components.
The metallic casing 10a is made from a preform 10b (shown in FIG. 7). The preform 10b is made from a metal plate by a drawing process. The preform 10b includes an approximately rectangular base 11b, a first sidewall 12b, a second sidewall 13b, a third sidewall 14b, and a fourth sidewall 15b. The first sidewall 12b, the second sidewall 13b, the third sidewall 14b, and the fourth sidewall 15b all extend around a periphery of the base 11b. The first sidewall 12b, the second sidewall 13b, the third sidewall 14b, and the fourth sidewall 15b respectively connect to each other. The first sidewall 12b, the second sidewall 13b, the third sidewall 14b, the fourth sidewall 15b, and the base 11b cooperatively define a cavity with an opening. An end of each of the first sidewall 12b, the second sidewall 13b, the third sidewall 14b, and the fourth sidewall 15b bends outward and respectively forms a first excess 121b, a second excess 131b, a third excess 141b, and a fourth excess 151b. The first excess 121b, the second excess 131b, the third excess 141b, and the fourth excess 151b respectively connect to each other. Each of the first excess 121b, the second excess 131b, the third excess 141b, the fourth excess 151b, and the base 11b form a corresponding connecting portion 122b, 132b, 142b, and 152b. In other words, the preform 10b includes an article portion and an excess portion. The article portion of the preform 10b consists of the base 11b and the sidewalls 12b, 13b, 14b, 15b. The excess portion of the preform 10b consists of the excesses 121b, 131b, 141b, 151b. 
Also referring to FIG. 8, an apparatus 100 includes an upper mold 110, a lower mold 130, and a positioning member 150. The upper mold 110 is opposite to the lower mold 130, and the upper mold 110 is movable relative to the lower mold 130. The upper mold 110 defines a rectangular depression (not labeled) opposite to the lower mold 130. The rectangular depression forms a first side surface 112, a second side surface 113, a third side surface 114, and a fourth side surface 115. The first side surface 112, the second side surface 113, the third side surface 114, and the fourth side surface 115 respectively connect to each other. The side surface 112, 113, 114, and 115 respectively forms a first sharp edge 1121, a second sharp edge 1131, a third sharp edge 1141, and a fourth sharp edge 1151. The first sharp edge 1121, the second sharp edge 1131, the third sharp edge 1141, and the fourth sharp edge 1151 respectively connect to each other. The lower mold 130 includes cutting side 131. The cutting side 131 includes a first cutting edge 132, a second cutting edge 133, a third cutting edge 134, and a fourth cutting edge 135. The first cutting edge 132, the second cutting edge 133, the third cutting edge 134, and the fourth cutting edge 135 correspond to the first sharp edge 1121, the second sharp edge 1131, the third sharp edge 1141, and the fourth sharp edge 1151, respectively. A horizontal width of the first cutting edge 132 is substantially equal to that of the first sharp edge 1121. A horizontal width of the second cutting edge 133 is substantially equal to that of the second sharp edge 1131. A horizontal width of the third cutting edge 134 is substantially equal to that of the third sharp edge 1141. A horizontal width of the fourth cutting edge 135 is substantially equal to that of the fourth sharp edge 1151.
In a process of making the metallic casing 10a shown in FIG. 6, the preform 10b is placed into the rectangular depression of the upper mold 110. The connecting portions 122b, 132b, 142b, 152b are located at the cutting edges 1121, 1131, 1141, 1151 respectively. The positioning member 150 is placed into the cavity of the preform 10b so that the preform 10b is fixed in the rectangular depression of the upper mold 110.
The upper mold 110 moves vertically to the lower mold 130 to keep the first sharp edge 1121, the second sharp edge 1131, the third sharp edge 1141, and the fourth sharp edge 1151 substantially coplanar with the first cutting edge 132, the second cutting edge 133, the third cutting edge 134, and the fourth cutting edge 135, respectively. The lower mold 130 moves horizontally in a first direction at a predetermined distance such that the first cutting edge 132 moves beyond the first sharp edge 1121. Thus, the first excess 121b is sliced from the first sidewall 12b. Similarly, the lower mold 130 moves horizontally in a second, third, and fourth direction at a predetermined distance in that order, such that the second cutting edge 133, the third cutting edge 134, and the fourth cutting edge 135 moves beyond the second sharp edge 1131, the third sharp edge 1141, and the fourth sharp edge 1151. Thus the second excess 131b, the third excess 141b, and the fourth excess 15 lb are sliced from the second sidewall 13b, the third sidewall 14b, and the fourth sidewall 15b, respectively. The rotary cutting process is completed, thereby yielding an article 10c (shown in FIG. 9). After that, the first sidewall 12b defines a slot 123 for receiving electronic components such as a connector. Thus, a metallic casing 10a is formed.
In a process of making the metallic casing 10a, the first excess 121b, the second excess 131b, the third excess 141b, and the fourth excess 151b respectively connect to each other. After the first excess 121b, the second excess 131b, and the third excess 141b are sliced from the preform 10b, the excess portion of the preform 10b is not separated from the preform 10b completely because the fourth excess 151b of the excess portion is still connected with the fourth sidewall 15. When the fourth excess 151b is sliced from the preform 10b, the excess portion of the preform 10b is separated from the preform 10b completely. The location where the excess portion is completely separated from the preform 10b is at a boundary between the first sidewall 12b and the fourth sidewall 15b. The excess portion of the preform 10b moves together with the lower mold 130 at the moment that the fourth excess 151b separates from the preform 10b, thereby generating a tearing effect to the boundary between the first sidewall 12b and the fourth sidewall 15b. Hence, after the rotary cutting process is completed, a gap 16b is formed at the top edge of the boundary between the first sidewall 12b and the fourth sidewall 15b. The gap 16b makes a case made from the preform 10b having poor appearance. Thus an extra process, such as polishing, is required to remove the gap 16b. 
Therefore, a new method and apparatus is desired in order to overcome the above-described shortcomings.